Embodiments of the invention relate generally to vehicle drive systems and, more specifically, to controlling an energy management system to optimize the cycle life of an energy storage device in a vehicle or non-vehicle system.
Electric vehicles and hybrid electric vehicles are typically powered by one or more energy storage devices, either alone or in combination with an internal combustion engine. In pure electric vehicles, the one or more energy storage devices powers the entire drive system, thereby eliminating the need for an internal combustion engine. Hybrid electric vehicles, on the other hand, include energy storage device power to supplement power supplied by an internal combustion engine, which greatly increases the fuel efficiency of the internal combustion engine and of the vehicle. Traditionally, the energy storage devices in electric or hybrid electric propulsion systems include batteries, ultracapacitors, flywheels, or a combination of these elements in order to provide sufficient energy to power an electric motor.
When two or more energy sources are used to provide power to drive system, the energy sources are typically well-suited to provide different types of power. A first energy source, for example, may be a high energy source that is more efficient at providing long-term power while a second energy source may be a high specific-power source more efficient at providing short-term power. The high specific-power source may be used to assist the high energy source in providing power to the system during, for example, acceleration or pulsed load events. Often, the high specific-energy source has a charge/discharge cycle life that is lower than the cycle life of the high power source.
One approach to increasing the cycle life of the high energy source may include increasing the size and/or energy rating of the source. However, increasing any of these parameters typically leads to an increased cost and weight of the high energy source and may potentially reduce acceleration rates if used in a vehicle application.
Therefore, it is desirable to provide a system that controls energy flow in a multi-source system to optimize the cycle lives of the power/energy sources used to deliver power to drive loads.